1. Field of the Invention
The present invention relates to a fuel injection control system for an internal combustion engine. More particularly, the present invention relates to a fuel injection control system for correcting a fuel injection quantity on the basis of a gear position.
2. Description of Background Art
A basic injection quantity of fuel is preferably determined on the basis of an intake air quantity. A technique has been disclosed in which manifold air pressure capable of accurately representing the intake air quantity has been adopted as a parameter for determining the basic injection quantity. On the other hand, in a motorcycle, the response to opening a throttle valve is an important aspect of operating performance and marketability as a whole. However, a manifold air pressure sensor does not provide an excellent output response to a change in negative pressure during transient driving, such as when the throttle is suddenly opened. Accordingly, it becomes difficult to accurately represent the intake air quantity.
In order to solve such a technical problem, for example, Japanese Patent Laid-Open No. 4-365943 discloses a technique in which a throttle opening θTH is newly added as a parameter for determining the basic injection quantity of fuel. The basic injection quantity is retrieved in a steady state from a manifold air pressure map (PB map) in which the engine speed NE and the manifold air pressure PB are used as parameters. In a transient state, the basic injection quantity is retrieved from a throttle opening map (TH map) in which the engine speed NE and the throttle opening θTH are used as parameters.
According to the background art technique described above, when an attempt is made to determine the basic injection quantity on the basis of the TH map, the basic injection quantity will be uniquely determined if the engine speed NE and the throttle opening θTH are obtained. However, when the gear position is low (speed reducing ratio is large) even if the engine speed NE and the throttle opening θTH are the same, running resistance (engine load) becomes lower than at a high gear position (speed reducing ratio is small). Therefore, it is preferable to differentiate the basic injection quantity in accordance with the gear position. However, if an attempt is made to provide the TH map for each gear position, there has been a technical problem in that numerous memory areas become necessary.